The invention thus is based on gearlike abrasive tools, as they are generally known for the precision working of the flanks of gears (U.S. Pat. No. 3,092,934, German OS No. 27 19 524). For dressing of the tool tooth flanks, one generally used a dressing tool having a gearlike constructed base member, the tooth flanks of which are coated with CBN or diamond granules. Precision working tool and dressing tool are for this purpose brought into a mating mesh. If work is thereby done without backlash, then forces act onto both sides of the teeth which are in mesh, which forces--depending on how many flanks are participating momentarily in the engagement--change constantly. These changing forces cause errors on the flanks of the precision tool, which are later transferred onto the tools which are to be worked thereby. Whereas if dressing is done with the single-flank contact, then the dressing tool so to speak follows the flank errors which exist on the precision working tool and does not eliminate them.
Therefore, the basic purpose of the invention is to improve the dressing task in such a manner that up to now occurring shortcomings are avoided. Furthermore, the precision working tool which is to be dressed and the dressing tool are designed such that they can be utilized for facilitating an improved dressing method.
To attain the aforesaid purpose, a precision working tool is provided wherein at least one guide gear is arranged next to the tool in axial direction. An adjusting device is provided for relatively rotatably connecting the tool and the guide gear together, the guide gear engaging during dressing of the tool tooth flanks a guide pinion arranged in axial direction next to a dressing tool and is connected thereto by structure preventing a relative rotation therebetween. A corresponding dressing tool is provided wherein at least one guide pinion is arranged in axial direction next to the dressing tool and is fixedly connected against relative rotation, the guide pinion engaging a guide gear arranged in axial direction next to a precision working tool which is to be dressed. Adjusting structure is provided for relatively rotatably connecting the tool and the guide gear together. The dressing itself occurs then according to a method explained in greater detail hereinbelow. Compared with the up to now common dressing, the inventive method is characterized by providing between the precision working tool which is to be dressed and the dressing tool backlash, however, the dressing itself occurs without backlash. Since the guide gear and the guide pinion can be manufactured very precisely, a very good flank shape on the precision working tool is produced during dressing, because the shape of the guide gear flanks is transferred onto the precision working tool.
The use of guide gears is known for the precision working of gears from U.S. application Ser. No. 576,672, filed Feb. 3, 1984, which application was abandoned in favor of U.S. application Ser. No. 816,946, filed Jan. 6, 1986 and assigned to the same assignee as the present invention. The machine on which this precision working is carried out must, however, be set up for the coaxial receiving of the guide gear pair and must have the necessary devices in order to be able to change the flank contact in the guide gear pair and in the tool-workpiece pair. Whereas, in the inventive precision working tool, the dressing tool and the inventive dressing method can be used or carried out on each known gear precision working machine.
U.S. application Ser. No. 664,811, filed Oct. 25, 1984 which application was abandoned in favor of U.S. application Ser. No. 853,088, filed Apr. 17, 1986 and assigned to the same assignee as the present invention, discloses a dressing tool which is fixedly connected to a guide gear, which dressing tool also engages the tooth system of a gearlike tool which is to be dressed. The guide gear serves the purpose of replacing the teeth which are missing in the dressing tool. Through its engagement with the tool gear tooth system it is exposed to a certain wear. This known guide gear therefore cannot be compared neither from its purpose nor from its operation with the inventive arrangement of the guide gears.
The precision working tool with its guide gear and/or the dressing tool with its guide pinion can, depending on the workpieces which are to be worked, have the shape of straight or helically toothed spur gears or of straight or spirally toothed bevel gears; they also can be internally toothed.
The number of teeth on the precision working tool and of the dressing tool does not need to correspond with the number of teeth on the guide gears. It can even be more favorable if they are different, because possibly existing pitch errors are then compensated for. It is only important that the two gear ratios are the same. If, for example, the precision working tool has 105 teeth and the dressing tool 39 teeth, then the guide gears must not have the same tooth counts. They may then for example have 70 and 26 teeth, which results in the same gear ratio.
If the dressing of the precision working tools occurs on a machine in which the tool and the workpiece approach one another in axial direction and are brought into meshing engagement, then it is preferable, in order to protect the axial tooth edges, to slope or round the edges, depending on the direction of movement.